1. Field of the Invention
The present invention relates to burst mode optical receivers, and more particularly to a burst mode optical receiver for determining whether an input signal is present and independently generating a reset signal for the initialization of an inter-packet period in accordance with the determined result.
2. Description of the Related Art
In order to transfer a large amount of information more rapidly to subscribers, a next-generation communication system known as an FTTH (fiber to the home) system, which includes an optical line installed up to each home, has been introduced. However, the FTTH system has drawbacks in that a high cost is involved in replacing the existing subscriber networks of copper wires. In this regard, a passive optical network (PON) is taken into consideration for the implementation of FTTH system at a much lower cost.
FIG. 1 illustrates the construction of a passive optical network. As shown in this drawing, the passive optical network comprises an OLT (Optical Line Termination) in a central office, a 1×N-passive optical splitter, and a plurality of ONUs (Optical Network Units) of subscribers.
In an optical multi-connection network, such as the passive optical network, each node transfers a packet or data to another node using a predetermined time slot. This optical multi-connection network is different from an existing point-to-point link in that the received data or packets are different in amplitude and phase from one another due to the optical losses occurring on different transfer paths. Such data is typically called burst mode data. In other words, when a plurality of subscribers transmits data via a single optical line in a time division multiplex manner, the receiver, OLT, perceives as if each subscriber sends data at a random time. Further, the incoming data packets are not constant in amplitude due to differences in the paths to the respective subscribers.
As a result, a burst mode optical receiver has recently been used which is configured to receive burst mode data that is different in amplitude and phase on a packet basis but restores the received burst mode data such that their packets are the same in amplitude and phase. In this regards, the burst mode optical receiver removes a DC blocking capacitor used in an AC coupling scheme of a conventional receiver to prevent the losses of burst mode data resulting from charging/discharging times of the capacitor. The burst mode optical receiver also functions to extract a detection threshold as a reference signal for data detection from each received burst mode packet and also functions to restore data by amplifying it symmetrically with respect to the extracted detection threshold.
FIG. 2 schematically shows the construction of a conventional burst mode optical receiver. As shown in this drawing, the conventional burst mode optical receiver comprises an optical detector 10, a preamplifier or trans-impedance amplifier (TIA) 1, an automatic threshold controller (ATC) 2, and a limiting amplifier 3.
In operation, the optical detector 10 converts an input optical signal into a current signal. The TIA 1 functions to convert the current signal converted by the optical detector 10 into a voltage signal. A trans-impedance, which is an input current-to-output voltage ratio, is determined by a feedback resistor Rf connected between an input terminal of the TIA 1 and an output terminal thereof. Note that the TIA 1 is used in a DC coupling manner. The input signal is amplified by the TIA 1 and then branches off into two parts. One part is inputted to the ATC 2, which then extracts a detection threshold of a received packet therefrom. The other part is DC-coupled and inputted to the limiting amplifier 3. The detection threshold, which changes according to the amplitude of the corresponding packet, is inputted to the Vref of the limiting amplifier 3. The limiting amplifier 3 functions to amplify signals of different amplitudes inputted thereto to restore them to ones of a constant amplitude using the Vref.
However, the conventional burst mode optical receiver has a disadvantage in that a reset signal for initialization in an inter-packet period is inputted via an external additional circuit, which in turn making it difficult to control the reset timing accurately. Moreover, the use of the external additional circuit makes the receiver circuitry complicated and increases the size of the receiver components.